bug#40205: 28.0.50; 32bit or LTO movemail build fails on macOS

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

On macOS, movemail cannot be built with CC='cc -arch i386':

    CCLD     movemail
  Undefined symbols for architecture i386:
    "_rpl_getopt$UNIX2003", referenced from:
	_main in movemail-1f1ea0.o
  ld: symbol(s) not found for architecture i386
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  make[1]: *** [movemail] Error 1
  make: *** [lib-src] Error 2

This is due to the following part in the system getopt.h:

  #ifndef _GETOPT
  #define	_GETOPT
  int	 getopt(int, char * const [], const char *) __DARWIN_ALIAS(getopt);

  extern char *optarg;			/* getopt(3) external variables */
  extern int optind, opterr, optopt;
  #endif

which is expanded to:

  int rpl_getopt(int, char * const [], const char *) __asm("_" "rpl_getopt" "$UNIX2003");

  extern char *rpl_optarg;
  extern int rpl_optind, rpl_opterr, rpl_optopt;

I think the Gnulib getopt does not expect the __asm line above.

64-bit LTO build with CC='cc -flto' fails, too.

    CCLD     movemail
  ld: reference to symbol (which has not been assigned an address) _rpl_getopt in '_main' from /var/folders/69/m7h39yv92g70qy7p3xdlghdm0000gn/T/cc-907a5d.o for architecture x86_64
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  make[1]: *** [movemail] Error 1
  make: *** [lib-src] Error 2

				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp